I 



PART II. POLAR MAGNETIC PHENOMENA AND TERRELLA EXPERIMENTS. CHAP. I. 399 



nature of the curves seems to indicate that the polar system of precipitation is at no great distance from 

 the station. This is especially evident in the declination. At first the deflections are mainly directed 

 eastwards, but subsequently change, and from about I3 h 30'" until the close of the period, are directed 

 westwards. The strength of the deflections is considerable, and as early as 15'' they have attained 

 a magnitude of the same order that we are accustomed to find during the polar storms in these regions. 



At the other polar stations there are no specially marked effects of polar storms until about i6 h 30, 

 so that up to that time the storm is concentrated about the districts surrounding Kingua Fjord. Even at 

 Godthaab there are no distinct effects of the storm. 



Continuing still westwards from Kingua Fjord through North America, we come to Fort Rae and 

 Uglaamie. Here the effect of the equatorial storm seems once more to be more evident. In the hori- 

 zontal intensity we find, at about io h 2o m , an impulse exactly similar to that at the other stations at which 

 the equatorial storm occurs; and after this we find, during the time that the equatorial storm is going 

 on, mainly positive deflections of more or less constant amplitude, and as regards strength very much 

 what one would expect to find them. There are, however, quite distinct effects of other systems. In 

 two or three places, for instance, we find in the horizontal-intensity curve, deflections to the opposite 

 side; and there are also sometimes impulses that are in all probability too powerful to be the direct 

 effect of the equatorial current-system. This circumstance is most clearly apparent in the declination- 

 curve. It is most natural here to assume that there is polar precipitation in addition to the equatorial 

 system. 



The most interesting feature here is, as we have said, the pronounced polar storm at Kingua 

 Fjord. It is fairly powerful, but of very limited area, and recalls in a striking manner circumstances 

 that we have previously found in our experiments. 



We see, for instance, in this connection, in looking at fig. 37 on page 80, Part I, that in addition 

 to the equatorial ring that is formed, there is a very distinct patch of light in the polar region, and 

 some fainter, less distinct polar precipitation more on the noon or morning side of the terrella. This 

 clear, sharply-defined patch answers to rays that descend towards the earth and leave it again in paths 

 that lie comparatively close together. A system of precipitation of this form, in the immediate vicinity 

 of the patch, will probably exert a considerable magnetic influence; but this will rapidly decrease with 

 increasing distance from the patch. It is just an effect such as this that we appear to have at Kingua 

 Fjord. There are, as we have said, powerful perturbing forces, which indicate comparatively abundant 

 polar precipitation, while the effect of this precipitation at a station no farther off than Godthaab, is 

 scarcely traceable. Lastly, if we look at the position of the patch in the figure, in relation to the mag- 

 netic pole of the terrella and the direction to the cathode, and imagine where this patch would fall if the 

 earth and its magnetic axis were to take the place of the terrella and its magnetic axis, and the direction 

 to the sun that to the cathode, it will easily be seen that the patch would fall more or less in the region 

 round Kingua Fjord. It thus seems very probable that this is an in-drawing of rays such as we find 

 by experiment. As we have said, there arc also certain effects of polar precipitation at Fort Rae and 

 Uglaamie, which may be connected with the slighter polar precipitation seen in the figure to the left of 

 the distinct polar patch. The latter, however, may possibly be a more or less accidental resemblance; 

 but the subsequent experiments may perhaps give fuller information regarding this circumstance. 



With regard to the occurrence of the comparatively powerful polar storm at Kingua Fjord simul- 

 taneously with the equatorial storm, we may remind the reader of the various more or less abnormal 

 conditions that we have come across at the American stations during the equatorial storms described in 

 Part I. Of these we will mention the storms of the 23rd and 24th November, 1902, described on pages 

 273 and 274 in which these abnormal conditions were very greatly developed, and also the storms of 

 the 26th January, 1903 page 67 and the 22nd March, 1903 page 128. 



